With the increasing requirement for the outstanding property and the reliable of the UPS, the wireless load-sharing technique is broadly used in many products. The wireless load-sharing means that each of the parallel inverters can provide the active power and reactive power to the loads in ratio without the communication bus.
For achieving the actually redundancy state, the conventional techniques has provided several wireless controlling techniques. Please refer to U.S. Pat. No. 5,745,356 and U.S. Pat. No. 6,381,157B2.
In the known wireless parallel system, the controlling methods thereof are from the traditional droop method, for example U.S. Pat. No. 6,803,679B1. For gaining the well power sharing, the controlling circuit droops directly against the frequency and the amplitude of the output voltage from the inverter to achieve the purpose, load-sharing. However, this kind of wireless parallel technique has at least one huge problem, i.e. the components parameters between the inverters are inconsistent. The inconsistent parameters affect the accuracy of the load-sharing precision between the inverters.
As above-mentioned, in order to avoid the mistakes resulting from the inconsistent parameters, the parallel inverters and the controlling method thereof are provided in the present invention.